"We claim responsibility for the suicide attack on the vehicle of the judiciary. The man who carried out the suicide attack was the brave warrior Sabir Swati," the group said in a statement, as it warned of further attacks.

"Remember that the Pakistani judiciary and those [...] who work for it are an obstacle to the imposition of an Islamic system. These people are the reason for mujahideen [fighters] being imprisoned or executed."

The attacker, who rammed his motorcycle into the van, appeared to be targeting government judicial employees in the Hayatabad area, police officials said.

"There was a suicide bomber on a motorcycle … the driver of the van has been killed, and four others have been wounded," said senior police official Sajjad Ahmed, speaking to media at the site of the explosion.

Tauheed Zulfiqar, a spokesman for the nearby Hayatabad Medical Complex where the wounded were being treated, confirmed the death toll.

Images of the blast showed the mangled wreckage of the van crashed into a low wall, with its windows and doors badly damaged.

Police cordoned off the site and deployed a security perimeter.

"We have found body parts of the bomber as well as his motorcycle, which hit the van," said Ahmed. "We have started a search operation, we will be able to share more information after it is completed."

Muhammad Tahir, Peshawar's police chief, said: "The initial analysis shows that at least 15kg of explosives were used in this attack."

Prominent opposition politician Imran Khan was due to visit the nearby Hayatabad Medical Complex later in the day, and police had been directed to secure the area.

A bomb disposal unit team and additional security had been dispatched to the area hours earlier, police sources said.

"Security was on high alert, because [Imran Khan] had to go to this hospital," provincial Information Minister Mushtaq Ghani told local television channel Dawn.